The progress of electronic devices such as mobile telephones and personal computers demands that secondary batteries used in these devices should be small-sized and reduced in weight. As examples of high-density secondary batteries which can meet this demand, lithium ion batteries are given. On the other hand, secondary batteries such as lead-acid batteries and nickel metal hydride batteries are used as large-sized and large-capacity power sources represented by electric cars, hybrid vehicles, electric motorcycles, and forklifts. Enthusiastic development has been recently made towards the adoption of a lithium ion secondary battery having a high energy density. In light of this, the lithium ion secondary battery is under development to attain a large-sized and large-capacity one, taking long life and safety into account.
As the power sources for these applications, a battery pack is used in which many batteries connected in series or parallel to each other are accommodated because it has a high driving power.
The quantity of current extracted from individual batteries is increased along with advancement in upsizing and large-capacitization of a battery. For this, it is desirable to limit the Joule calorific value of an external terminal to a lower level.
Further, though battery external terminals are connected to each other by external leads to connect batteries in series or parallel, the stress applied to the external leads is directly applied to positive electrode terminals and negative electrode terminals and rotates the positive electrode and negative electrode terminals, prompting fears as to the dangers of external short-circuit failures.
Patent Literature 1 relates to a current collecting system of a battery or capacitor. Patent Literature 2, in turn, relates to a rectangular type secondary battery.